Combined inert gas recirculation and tar heater operation



March 23, 1937.

G. T. GAMBRILL. JR

COMBINED INERT GAS RECIRCULATION AND, TAR HEATER OPERATION Filed NOV. 30, 1923 Condenser I5 Sheets-Sheet 1 flaw Tar ffaraye I Wafer foo/ed (aw arena!- 1 690/199 720/21 Gembri/(Ji:

svipA/f ATTORNEY G. T. GAMBRILL, JR 2,074,689 I COMBINED INERT GAS RECIRCULATION AND TAR HEATER OPERATION March 23, 1937.

Filed Nov. so, 1922 3 Sheets-Sheet 2 lulu @QEQQ INVENTOR Georg; mamas Gambr/l/ J73 BY WA ATTQRNE Patented Mar. 23, 1937 UNITED STATES PATENT OFFICE George Thomas Gambrill, Jr., Birmingham, Ala., assignor to The Barrett Company, New York, N. Y., a corporation of New Jersey Application November 30, 1928, Serial No. 322,843

2 Claims.

This invention relates to the distillation of tar to separate volatile constituents therefrom, and particularly to improvements in the method and apparatus utilized in conducting the distillation.

5 In the distillation of tar, particularly coal tar, as heretofore practised it has been customary to subject the tar to initial heating in a tubular still to a temperature above that at which vapors normally separate from the tar. The tar is delivered continuously to the still and is similarly withdrawn and carried to a vapor box in which the vapors are permitted to separate. The vapors are conveyed to a condenser. The partially distilled tar is then delivered to a receiver in which it is maintained at a relatively high temperature.

The tar is withdrawn from time to time and is subjected to further heating in a still and is simultaneously blown with an inert gas such as air to facilitate the removal of additional vapors.

The operation as described involves two distinct distillations and the necessity for supplying the heat required therefor. Furthermore, the operation is intermittent and uneconomical because of the heat losses incurred necessarily therein.

It is the object of the present invention to provide a method and apparatus wherein tar is distilled continuously and with the minimum expenditure of heat, the distillation being effected to separate the vapors and to produce pitch of the desired characteristics while avoiding losses incident to the operation as heretofore conducted.

A further object of the invention is the utilization of an inert gas to facilitate the initial separation of vapors from the tar as it is delivered from the still, whereby pitch of the desired quality is obtained without reheating the tar.

In carrying out the invention, I employ a suitable still, preferably of the tubular type, through which tar is circulated continuously. The still 0 may be heated by combustion gases or otherwise to bring the tar to the required temperature. The heated tar is delivered to a vapor box where the vapors separate therefrom thus forming a pitch residue which is subjected therein to a rel- 4 atively large volume of an inert gas such as air, steam or other gas which is chemically inert with respect to the pitch at the temperatures prevailing in the vapor box. The gas is distributed through the pitch and facilitates the separation 5 of the vapors therefrom, so that substantially all of the vapors are removed, leaving pitch of the desired quality which may be delivered directly to the pitch bay or pitch machine or may be utilized otherwise as may be desired. The inert 55 gas with the vapors is withdrawn from the vapor box and cooled in a suitable condenser, preferably by heat interchange with cool tar which is being supplied to the still. The inert gas and vapors are conveyed thence 'to a second condenser and are cooled therein to a temperature such that the volatile constituents are condensed. The con- 5 densate may be separated then from the inert gases,which may be delivered to a compressor and returned thence to the vapor box for further utilization. The inert gas travels, therefore, in a closed cycle through the'vapor box and con- 5 denses to the compressor which returns it to the vapor box.

A further improvement is effected by preheating the inert gas to a temperature preferably 15 equal to or even higher than the temperature of r the pitch in the vapor box before the gas is mingled with the pitch, to facilitate the removal of vapor therefrom. The preheating of the gas may be accomplished in any desired manner, for example by heat exchange with the mixture of inert gas and vapor from the vapor box. It may be heated, likewise, by heat exchange with flue gases from the tar still or by a separate heater supplied with fuel for the purpose of bringing the gas to the desired temperature before it enters the vapor box. The preheating of the gas is particularly desirable since it ensures the effective separation of the vapors from the pitch andfpermits the production of pitch of higher melting point than could be obtained otherwise.

The method as described has numerous advantages, including reduction of time during which the tar is maintained at a temperature capable of effecting decomposition, increase in the yield of condensate, reduction in the quantity of fuel used per gallon of tar distilled, elimination of the second still and consequent avoidance of the initial cost and the expense of operation thereof, and reduction of the other equipment and of the quantity of material necessarily transferred by pumps in the system. The operation is simplified and is continuous, and affords a satisfactory and "economical procedure whereby the maximum yield of condensate and pitch is secured at the minimum of expense.

The invention will be more readily understood by reference to the following detailed description thereof when read in connection with the accompanying drawings, in which Fig. l is a diagrammatic representation of a distillation plant embodying the invention,

Fig. 2 is a similar representation of a plant showing an arrangement for the preheating of the inert gas,

Fig. 3 is a diagrammatic representation of a plant showing a modified arrangement for the preheating of the inert gas, and

Fig. 4 illustrates a further modified arrange- 5 ment for preheating the inert gas.

Referring to Fig. 1, 5 indicates a still having tubes 6 therein through which tar is circulated and subjected to combustion gases supplied by a furnace "l, the tar being thereby heated to the temperature required for the separation of the volatile constituents. The exact temperature employed will vary with the character of the tar treated, and the production of combustion gases, as well as the rate of travel of the tar through the still, is regulated so that the tar is raised to the desired temperature. The tar is delivered through a pipe 8 to a vapor box 9v which is supplied with a suitable inert gas such as air through a pipe Ill. The gas is distributed through the pitch in the vapor box by a distributor II so that the pitch is subjected uniformly to the effect of the inert gas. The pitch is maintained in the vapor box at a substantially uniform level, and the vapor separated from the tar together with the inert gas is withdrawn through a pipe l2. The pitch is likewise withdrawn continuously through a pipe 13 and is delivered thereby toa pitch bay (not shown) or any suitable receptacle therefor. The gas and vapors enter a condenser I4 and are cooled therein by heat exchange with tar which is delivered to the condenserthrough a pipe I5 and withdrawn through a pipe IS. The tar which is thus heated isconveyed through a pipe I! to the tubes 6 of the still. The tar is supplied to the condenser by a pump 18 from a storage tank IS, the supply being regulated so as to maintain a proper flow of the tar through the still.

The partially cooledgas and vapors from the condenser 14 are delivered through a pipe 20 to a coil 2| in a condenser 22 which is supplied with a suitable cooling agent such as water to reduce the temperature of thegas and-vapors to a point at which the vapors are condensed. .The condensate with the inert gas passes through a pipe 23 to a separator 24 in which the eondensate separates. The condensate is withdrawn through apipe 25 and may be delivered to suitable receptacles 26. The inert gas passes through a pipe 27 to a compressor 28 which delivers it to the pipe I0 and thence to'the vapor box, thus completing the cycle and permitting the treatment of additional quantities of tar supplied from the still in the vapor box. This operation permits the continuous withdrawal of vapors from the vapor box and the production therein of pitch which is likewise withdrawn continuously. The efliciency of the operation as described v may be increased by preheating the inert gas before it enters the vapor box as indicated in Fig. 2 of the drawings. In the apparatus illustrated therein, the still 30 is provided with a coil 3| through which the tar is circulated, being heated therein by combustion gases supplied from a furnace 32. The heated tar is delivered through a pipe 33 to a vapor box 34 and is subjected therein to inert gas supplied through a pipe'35 to .a distributor 35. The vapors with the inert gas are withdrawn through a pipe 31 and enter a condenser 38 where they are partially cooled by heat exchange. with tar delivered to the condenser through a pipe 39. and withdrawn through a pipe 48. The tar thus partially heated is conveyed by a pipe 4| to the coil 3| in the still.

"'75 The vapors pass from the condenser 38 through a pipe 42 to a condenser 43 having a coil 44 which is cooled by any suitable medium such as water so that the vapors are reduced to the temperature at which they condense. The inert gas and the condensate pass through a pipe 45 to a separator 46 in which the condensate is separated. The condensate may be delivered through a pipe 4'! to receptacles 48 therefor. The inert gas passes then through a pipe 49 to a compressor 58 and thence through a heater 5|. The inert gas may be heated in any suitable manner as, for example, by heat exchange with combustion gases or gases from any other source, and are delivered through the pipe 35 to the vapor box, as hereinbefore described. The preheating of the gases ensures the separation of vapors from the heated pitch in the vapor box and facilitates the recovery of the vapors and the production of pitch having the desired characteristics. The pitch is withdrawn continuously through a pipe 52 and maybe delivered to a pitch bay (not shown) or utilized in any desired manner.

Alternatively, as shown in Fig. 3, the heating of the inert gas may be effected by delivering it from the compressor through a pipe 53 to a heat exchanger 54 through which the mixture of inert gas and vapor from the vapor box circulates before it enters the condenser 38. The compressed inert gas being thus preheated is delivered through the pipe 55 to the pipe 35 and thence to the vapor box.

In another alternative procedure illustrated in Fig. 4, the inert gas from thecompressor 50 is delivered through a pipe 56 to a heat exchanger 51 which may be heated by waste or flue gases from the furnace 32 or by radiant heat therein. The heated gas is delivered through a pipe 58 to the pipe 35 and thence to the vapor box.

The apparatus and procedure as described are merely illustrative of the application of the principle of the invention, which involves the introduction of an inert gas such as air to the vapor box in which the vapor is released from the previously heated tar. As herein indicated, greater efficiency is attained by preheating the inert gas before it enters the vapor box and the preheating may be accomplished in various Ways, either by supplying heat for that purpose or by utilizing heat which otherwise would be wasted. The method is particularly economical where waste heat is utilized in bringing the inert gas to the required temperature.

The apparatus and process described herein is particularly designed and adapted for the distillation of coal tar to obtain a pitch product of definite softening point. The following is given as an illustrative example of the operating conditions in the practice of the process which resulted in the formation of a pitch having a melting point of 164 F. The temperature of the tar entering the vapor box was 635 F., the temperature of the inert gas (air) entering the vapor box 325 F. and the temperature of the pitch withdrawn from the vapor box 560 F. A pressure of 1.5 inches of mercury was maintained in the vapor box. The heated tar and inert gas were continuously introduced into the vapor box and the pitch and mixture of inert gas and vapor continuously withdrawn therefrom. The inert gas was passed through the vapor box at the rate of about 43,200 cubic feet per hour calculated at 60 F. 311 cubic feet per hour of tar at 60 F. was introduced into the still so that for each cubic foot of tar introduced into the still approximately 138 cubic feet of inert gas was passed through the vapor box. An oil yield of 23.6% by volume, based on the total volume of the tar introduced in the still, was thus obtained. It is noted that this oil yield represents a substantial improvement over the oil yields obtained in the distillation of tar under corresponding conditions but omitting the feature of recirculating inert gas through the vapor box.

Numerous advantages of the invention have been indicated. and these and other advantages can be attained by the practice of the invention with various changes and modifications of the apparatus and procedure without departing from the invention.

I claim:

1. The method of distilling coal tar which comprises heating the tar while avoiding separation of the vapor therefrom, then releasing the vapor thus forming a pitch residue, and simultaneously blowing the pitch residue with an inert gas preheated to a temperature approximating that of the pitch, withdrawing the vapor and inert gas, cooling the mixture to separate condensable constituents, reheating the inert gas by heat exchange with the mixture of inert gas and vapors, and returning it for further contact with additional portions of the pitch residue.

2. The method of distilling tar and of producing distillate oils and pitch residues therefrom which comprises heating the tar to .a temperature such that a pitch residue will be formed upon release of vapors therefrom, avoiding separation of vapors from said tar during said heating step, then releasing the vapors thus forming a pitch residue, simultaneously with the release of the vapors contacting the resultant pitch residue with an incondensable inert gas preheated to a temperature at least as high as the temperature of said residue, withdrawing the mixture of vapors and incondensable inert gas and cooling-this mixture to separate the vapors from the inert gas, reheating the inert gas by heat exchange with the mixture of inert gas and vapors and returning it for further contact with additional portions of pitch residue.

GEORGE THOMAS GAMBRILL, .Jx. 

